Vehicle skid control system

A brake control system for a wheeled vehicle having first and second sets of wheels provided with first and second sets of wheel brakes, a brake pedal operable by the vehicle operator, a master cylinder connected with and actuated by the brake pedal to supply pressurized brake fluid in a first brake pressurizing circuit to actuate the first set of wheel brakes and to supply pressurized brake fluid in a second brake pressurizing circut to actuate the second set of wheel brakes, said second brake pressurizing circuit comprising;

• a normally open isolation valve means connected between the master cylinder and the seond set of wheel brakes;
• a normally closed dump valve means oonnected between the second set of wheel brakes and a fluid reservoir;
• and
• control means connected to operate said isolation valve means and said dump valve means, said control means including means for detecting a wheel lock-up condition of the second set of wheels and means for sensing the deceleration of the second set of wheels, said control means operable ot close said isolation valve to hold the fluid pressure to the second set of wheel brakes at a relatively constant level after said wheel lock-up conidition of the second set of wheels is detected, said control means operable to selectively open said dump valve means after said wheel lock-up condition has been detected to enable fluid to flow into said fluid reservoir to selectively reduce fluid pressure to the second set of wheel brakes and correct the lock-up condition of the associated wheel, said control means further operable to selectively open said isolation valve to selectively increase pressure to the wheel brake after said wheel lock-up condition has been corrected and the rate of change of decelertion of the associated wheel increases by a predetermined amount, said control means operable to selectively control the application of increased pressure to the associated wheel brake to prevent further lock-up of he associated wheel.

A method of braking at least one wheel of a multi-wheeled vehicle having means for supplying pressurized brake fluid to actuate a selected wheel brake, said method comprising the steps of:

• (a) supplying brake fluid at an increasing pressure to actuate the selected wheel brake and decelerate the associated wheel;
• (b) holding fluid pressure to the selected wheel brake at a relatively constant level after a wheel lock-up condition of the associated wheel is detected;
• (c) subseqent to step (b), selectively reducing fluid pressure to the selected wheel brake to correct the wheel lock-up condition;
• and
• (d) subseqent to step (c), selectively increasing fluid pressure to the selected wheel brake when the rate of change of deceleration of the associated wheel increases by a first predetermined amount.

In a wheeled vehicle having means for supplying pressurized brake fluid to actuate the associated wheel brakes of the vehicle, a brake control system for controlling the application of pressurized brake fluid to at least one selected wheel brake to control the braking of the associated wheel, said control system comprising:

• a normally open isolation valve means connected between the supply means and the selected wheel brake;
• a normally closed dump valve means connected between the selected wheel brake and a fluid reservoir;
• and
• control means connected to operate said isolation valve means and said dump valve means, means coupled to monitor the speed of the associated wheel for generating a wheel speed signal, means for generating a first slip signal when the difference between the wheel speed signal and a first speed ramp signal representing a first predetermined deceleration rate exceeds a predetermined slip threshold, means responsive to said first slip signal for closing said isolation valve, means for generating a second slip signal when the difference between the wheel speed signal and a second speed ramp signal representing a second predetermined deceleration rate greater than said first predetermined rate exceeds said predetermined slip threshold, and means responsive to said second slip signal for selectively opening said dump valve means after said isolation valve has been closed to enable fluid to flow into said fluid reservoir to selectively reduce fluid pressure to the selected wheel brake.

A brake control system for a wheeled vehicle having first and second sets of wheels provided with first and second sets of wheel brakes, a brake pedal operator, a master cylinder connected with and actuated by the brake pedal to supply pressurized brake fluid in a first brake pressurizing circuit to actuate the first set of wheel brakes and to supply pressurized brake fluid in a second brake pressurizing circuit to actuate the second set of wheel brakes, said second brake pressurizing circuit comprising:

• a normally open isolation valve means connected between the master cylinder and the second set of wheel brakes;
• a normally closed dump valve means connected between the second set of wheel brakes and a fluid reservoir;
• and
• control means connected to operate said isolation. valve means and said dump valve means, means coupled to monitor the speed of the associated wheel for generating a wheel speed signal, means for generating a first slip signal when the difference between the wheel speed signal and a first speed ramp signal representing a first predetermnied deceleration rate exceeds a predetermined slip threshold, means responsive to said first slip signal for closing said isolation valve, means for generating a second slip signal when the difference between the wheel speed signal and a second speed ramp signal representing a second predetermined deceleration rate greater than said first predetermined rate exceeds said predetermined slip threshold, and means responsive to said second slip signal for selectively opening said dump valve means after said isolation valve has been closed to enable fluid to flow into said fluid reservoir to selectively reduce fluid pressure to the second set of wheel brakes.

A method of braking at least one wheel of a multi-wheeled vehicle having means for supplying pressurized brake fluid to actuate a selected wheel brake, said method comprising the steps of:

• (a) supplying brake fluid at an increasing pressure to actuate the selected wheel brake and decelerate the associated wheel;
• (b) monitoring the speed of he associated wheel;
• (c) compairing the speed of the associated wheel with a first speed ramp signal representing a first predetermined deceleration rate;
• (d) holding pressure to the selected wheel brake at a relatively constant level after the difference between the associated wheel speed and the first speed ramp exceeds a predetermined slip threshold;
• (e) subsequent to step (d), comparing the speed of the associated wheel with a second speed ramp signal representing a second predetermined deceleration rate;
• and
• (f) selectively reducing pressure to the selected wheel brake when the difference between the associated wheel speed and the second speed ramp exceeds said predetermined slip threshold.